The present invention relates to anesthesia and respirator masks typically used in the medical arts
The section of the book by J. A. Dorsch et al, pp. 363-392 of "Understanding Anesthesia Equipment" (Williams & Wilkins, 1984) describes several popular types of anesthesia masks. An important aspect of the anesthesia mask noted on page 363 is that of the two types of face seal "One is a cushion (rim pad) that is inflated with air or filled with a material that will conform to the face when pressure is applied. The second type of seal is a flange that is an extension of the body." Masks that can be widened or narrowed to fit the face are shown in FIG. 13.1 and 13.2 are a hybrid of the above two types. The interior void which is inflated and extends from the face seal section of their double rubber shell construction up to the connector orifice. This type of mask is in contrast to those inflatable masks whose inflatable portion is separate from the dome or semi-spherical external support shell necessary to connect a flexible inflatable cuff with the connector orifice.
In the Dorsch book, the Laerdal mask of FIG. 13.8 is an example of the single support shell/inflatable cuff mask. It is further noted on page 367 that "The best fit is obtained by selecting a mask and testing it before induction of anesthesia. The smallest mask that will do the job is the most desirable because it will cause the least increase in dead space, will usually be easiest to hold, and will be less likely to result in pressure on the eyes." The very serious implications of failing to obtain a gas tight seal between the gas delivery conduits and the face of the wearer has made each of the above factors the focus of specific improvements in the art. The problems associated with masks in the art are shown and described on pages 367-368, especially directed to FIG. 13.11. In that FIG. 13.11, the Laerdal mask is shown being held in place with one hand, the most common and desirable method since the anesthesiologist or nurse will then have one hand free to use for other tasks. It will readily occur to the skilled person that there is tremendous potential for a failure to maintain a gas tight seal about the patient's mouth and nose, especially in the cheek area as the masseter/buccinator muscles form a rather softer area for which the seal must be maintained. The single support shell/inflatable cuff mask is especially prone to this failing due to the lack of sensible response of the separation of the inflated cuff from the cheek. The second type of mask described above may more readily alert the anesthesiologist or nurse of a gas seal break or leak in the cheek area because the edges of the firm face seal flange do not extend substantially outwardly beyond the effective sealing edge to obscure the flange/skin seal. However, an unsymmetrical facial bone structure or musculature of the patient or a failure to maintain a relatively narrow range of downward orientation of the non-inflatable cuff mask makes the flange type of mask more difficult to maintain in a gas tight seal than the mask with an inflatable cuff.
U.S. Pat. No. 790,057 shows an early inhaler anesthesia mask. A generally inward curvature is seen in FIG. 2 showing an adaptation for the bridge of the nose of a patient.
U.S. Pat. No. 1,206,045 shows a nasal inhaler with a hard, gas tight support shell with "flange" or plastic material to be situated between the shell and the patient as sealing means.
U.S. Pat. No. 2,313,999 generally shows a double shelled mask similar to that of FIG. 13.1 of the Dorsch book. The double shell comprises generally quite firm but flexible rubber and extends from the seal to the gas conduit at the orifice connector to the variable diameter expanded section at the face-contacting portion of the double shell. In contrast to the Laerdal mask shown in the Dorsch book downward pressure on the supports shell generally presses the "flange" face contact surface in a direction outward from the axis formed by the orifice connector. In another aspect of this outward motion of the sealing surface of the "flanges" of the non-inflatable cuff type mask, the skin of the patient is drawn away from the nose and mouth. The opposing action of reacting skin and musculature improves the pressure of and increases surface area of the sealing contact surface area between the mask and the patient.
U.S. Pat. Nos. 2,535,938, 2,625,155, 2,765,788 and 3,042,035 generally show masks with relatively hard "flange" material. So although downward pressure tends to increase the seal by causing a reaction of opposing skin and muscles, the relatively narrow "flange" material almost eliminates this advantage and, for the face with extensive wrinkling in old age, will tend to "trap" the creases in the skin between the harder "flange" material and permit gas to flow between the atmosphere into the mask or vice versa.
U.S. Pat. No. 2,875,757 describes an inflatable cuff type mask. FIG. 3 very clearly shows the cuff cross-section. FIG. 4 shows how the inflated cuff looks and presents an inward facing sealing surface. In a cross section of the mask through an axis formed through the axis of the orifice of the orifice connector, it is seen that the support shell outwardly and away from the orifice connector and over the inflatable cuff such that the bottom most extended surface of the inflated cuff extends only slightly beyond the rim of the support shell. Downward pressure on the outside of the mask to form a seal with the patient's face necessitates the inflated cuff be pressed inward. The greatest pressure that may be applied to such a mask is limited to that pressure within which the cuff will maintain a clearance between the patient's face and the hard support shell.
U.S. Pat. No. 3,982,532 shows another double shell mask construction where the void formed extends from the face contact surface to the orifice connector. With careful choice of materials and with regard to relative flexibility and curvature "memory", certain embodiments of the device in this patent may, upon downward pressure of the mask to the face of a patient, may move outwardly from the nose and mouth the skin and facial muscles.
U.S. Pat. No. 4,062,357 generally shows the Laerdal mask described above. It will be seen from FIGS. 3, 6, 7 and 8 that downward pressure application to the face of a patient will cause the inflated cuff to assume a generally elliptical cross-section whereby increasing downward pressure causes the ends of the ellipse to move roughly both inward, toward the axis of the general angle of the downward pressure, and outward, away from that axis and away from the patient's nose and mouth. The result of the relatively equal inward and outward force distribution on the inflated cuff is that almost only about half of the downward pressure is transmitted to an outward motion of the cuff to facilitate a reaction of the skin and muscle back toward the nose and mouth. This is an inherent disability since the skin and musculature extending from the contact surface of the inflated cuff to the nose and mouth of the patient are generally less reactive and somewhat more elastic in that direction than in the other direction.
U.S. Pat. No. 4,201,205 shows an oxygen mask with a single firm-flexible clear plastic shell with a "flange" for improving the seal between the wearer's face and the mask. This simple construction is consistent with the limited seal needed.
U.S. Pat. No. 4,347,205 shows an inflated cuff filled with a dual lumen.
U.S. Pat. No. 4,559,940 shows an inflatable chamber for occluding a patient's mouth during airway intubation.
U.S. Pat. No. 4,803,981 shows a nose inhaler comprising only a rather firm rubber foam material. Downward pressure would tend to, as with similar "flange" type masks, move skin and muscles away from the nose.
U.S. Pat. No. 4,913,401 discloses a valve assembly generally representative of inflating valves for inflatable cuffs.
U.S. Pat. No. 5,121,745 shows a collapsible inflatable cuff mask with equal-force distribution similar to that of the above Laerdal mask.
U.S. Design Pat. No. D293,613 show an inflatable cuff type mask with inflating valve located at the nose bridge area.
U.S. Design Pat. No. D323,908 show an inflatable cuff type mask with an extension of the support shell to be, in operation, located just superior to the bridge of the nose, and providing the middle finger of the anesthesiologist or nurse with improved support.
There is a need to provide an inflatable cuff type mask wherein the benefits of the "flange" type mask may be obtained while also obtaining the increased surface contact area provided by the inflatable cuff type masks.